Detection and measurement of an endogenous clonidine-displacing substance in human cerebrospinal fluid

Clonidine-displacing substance (CDS) is a novel endogenous ligand for clonidine receptors previously detected in bovine brain and human serum. We examined for the first time whether CDS can be detected and measured in human cerebrospinal fluid (CSF). Using the [³H]clonidine displacement assay, we found that CDS could be identified and quantified in each of the CSF samples obtained from 81 patients with various neurological disorders. Mean level of CDS in CSF was 4.66 units/ml. Exceedingly high levels were observed in the CSF of patients with neoplastic meningitis (mean, 36.75 units/ml) and stroke (mean, 19.5 units/ml) (P < 0.0001). No correlation was found between CDS levels in CSF and age, gender, CSF protein or number of cells. CDS levels in CSF were higher than those in the serum (P < 0.01). We conclude that CDS is present and can be measured in human CSF. High CDS levels in CSF from patients with leptomeningeal metastases may serve as a tumor marker for malignant infiltration of the meninges. Additional studies in stroke patients will determine whether this endogenous ligand plays a role in the pathogenesis of cerebral ischemia.